1. Field of the Invention
The present invention generally relates to quality of service on computer networks, such as the Internet. The present invention more particularly relates to managing bandwidth available amongst a set of network connections in order to improve quality of service of a computer network.
2. Discussion of Background
It is hard to dismiss the entrepreneurial nature of the Internet; this is no longer a research project. For most organizations connected to the global Internet, the Internet is a full-fledged business interest. Having said that, it is equally hard to dismiss the poor service quality that is frequently experienced. The rapid growth of the Internet, and increasing levels of traffic, make it difficult for Internet users to enjoy consistent and predictable end-to-end levels of service quality.
The Internet has historically offered a single level of service, that of “best-effort,” where all data packets are treated with equity in the network. However, we are finding that the Internet itself does not offer a single level of service quality, and some areas of the network exhibit high levels of congestion and consequently poor quality, while other areas display consistent levels of high quality service. Customers are now voicing a requirement to define a consistent service quality they wish to be provided, and network service providers are seeking ways in which to implement such a requirement. This effort is happening within the umbrella called “Quality of Service” (QoS). Examples of factors that affect QoS on the Internet include delay, bandwidth, and reliability.
Delay is the elapsed time for a packet to be passed from the sender, through the network, to the receiver. The higher the delay, the greater the stress that is placed on the transport protocol to operate efficiently. For Transfer Control Protocol (TCP), higher levels of delay imply greater amounts of data held “in transit” in the network, which in turn places stress on the counters and timers associated with the protocol. It should also be noted that TCP is a “self-clocking” protocol, where the sender's transmission rate is dynamically adjusted to the flow of signal information coming back from the receiver, via the reverse direction acknowledgments (ACK's), which notify the sender of successful reception. The greater the delay between sender and receiver, the more insensitive the feedback loop becomes, and therefore the protocol becomes more insensitive to short term dynamic changes in network load. For interactive voice and video applications, the introduction of delay causes the system to appear unresponsive.
Bandwidth is the maximal data transfer rate that can be sustained between two end points. It should be noted that this is limited not only by the physical infrastructure of the traffic path within the transit networks, which provides an upper bound to available bandwidth, but is also limited by the number of other flows which share common components of this selected end-to-end path.
Reliability is commonly considered a property of the transmission system, and in this context, it can be thought of as the average error rate of the medium. Reliability can also be a byproduct of the switching system. A poorly configured or poorly performing switching system can alter the order of packets in transit, delivering packets to the receiver in a different order than that of the original transmission by the sender, or even dropping packets through transient routing loops.
The Internet is composed of a collection of routers and transmission links. Routers receive an incoming packet, determine the next hop interface, and place the packet on the output queue for the selected interface. Transmission links have characteristics of delay, bandwidth and reliability. Poor service quality is typically encountered when the level of traffic selecting a particular hop exceeds the transmission bandwidth of the hop for an extended period time. In such cases, the router's output queues associated with the saturated transmission hop begin to fill, causing additional transit delay, until the point is reached where the queue is filled, and the router is then forced to discard packets or at least portions of packets (reduced reliability). This in turn forces adaptive flows to reduce their sending rate to minimize congestion loss, reducing the available bandwidth for the application.
Unfortunately, present methods of managing bandwidth that is available amongst a set of network connections have been inadequate, given the increasingly demanding transmission needs of users of the Internet.